The invention relates to a liquid crystal display device having a plurality of pixels, comprising a layer of nematic liquid crystal material between a first substrate which is provided with a first orientation layer inducing a first orientation direction and a tilt angle in the molecules of the liquid crystal material, and a second substrate which is provided with a second orientation layer inducing two orientation directions in the molecules of the liquid crystal material, so that a pixel is divided into two sub-pixels.
Display devices of this type are generally used in, for example, monitors, TV applications and, for example, in display devices for motorcars and instruments.
A display device of the type mentioned in the opening paragraph is described in "A Full-Color TFT-LCD with a Domain-Divided Twisted-Nematic Structure", SID 92 DIGEST, pp. 798-801. In the domain-divided twisted-nematic LCD described in this article, pixels are divided into sub-pixels so as to reduce the viewing angle dependence, with the angle dependence being different for both sub-pixels, which is achieved by introducing different orientation or tilt angles on a surface for different parts of a pixel. In the device shown in this article, this is realized for a part of the cell by providing an orientation layer, yielding a high tilt angle after rubbing, on a layer yielding a low tilt angle after rubbing.
A drawback of this method is that two different layers of different materials must be provided, usually a first (in)organic layer yielding a low (pre)tilt and then a second organic layer yielding a high (pre)tilt. This requires an additional photolithographic step (providing the photoresist, masking, illuminating, developing and finally stripping of the photoresist). Moreover, when these layers are rubbed for obtaining the ultimate tilt angle at the interfaces, the layers with the high and low (pre)tilts will mix so that undefined edges of sub-pixels are created. If such a substrate (as used in active matrix displays) is provided with switching elements, they may get damaged due to electrostatic aspects during rubbing. Also with other multidomain techniques such as, for example the amorphous TN effect, the viewing angle dependence may be reduced. However, display devices based on this effect have a low contrast due to the formation of reverse-tilt disclination lines during operation of such display devices. It is true that the contrast can be enhanced to some extent by adapting the production process, but this results in a grainy image because the separate TN domains become visible.